Neonatal seizures cause cerebral vascular endothelial injury and sustained loss of cerebral blood flow regulation. Our goal is to understand the endogenous mechanisms that may protect neonatal brain from long-term effects of seizures. This renewal application is based on our findings from past specific aims and novel exciting preliminary data that pinpoint the signaling mechanisms that may counteract adverse effects of seizures and promote cell survival in the neonatal cerebral circulation. Our preliminary data indicate: 1) seizures increase production of reactive oxygen species (ROS) in the cerebral vasculature, and 2) NADPH oxidase and the mitochondrial respiratory chain are major sources of cerebrovascular oxidative stress caused by excitotoxic levels of glutamate during seizures. Constitutive heme oxygenase (HO-2) is rapidly activated during seizures and provides a potent endogenous cytoprotective mechanism in the neonatal cerebral circulation. Astoundingly, our novel preliminary data indicate that ROS acutely increase HO-2 activity in the cerebral vasculature, suggesting HO-2 may be a redox-sensitive protein. The mechanisms of HO-2 redox regulation that counteracts the seizure-induced oxidative stress injury are not known. Therefore, we hypothesize that ROS are signaling molecules that increase the activity of HO-2 initiating a negative feedback antioxidant mechanism that promotes endothelial survival during neonatal seizure-induced cerebrovascular insult. To test this hypothesis, four specific aims will be addressed using newborn pigs in vivo, freshly isolated cerebral microvessels, and cerebral vascular endothelial cells in primary cultures: 1. Test, in vivo, the hypothesis that HO-2 is a redox-activated endogenous antioxidant enzyme essential for endothelial survival during neonatal seizures. 2. Test, in vivo, the hypothesis that antioxidant actions of CO and bilirubin, the products of HO-2 activity, are critical in improving long-term outcome from seizure-induced loss of cerebral vascular function. 3. Examine, in vitro, redox regulation of HO-2 activity in cerebrovascular endothelium. 4. Identify, in vitro, HO-2-mediated antioxidant mechanisms of cerebrovascular endothelial survival. These experiments are novel both by combining in vivo and in vitro approaches to study the endogenous mechanisms of cerebroprotection and to investigate, for the first time, the concept that HO-2 is a redox-activated endogenous antioxidant enzyme essential for cerebral endothelial cell survival during seizures. Disorders of the perinatal cerebral circulation are the most prominent cause of mortality and morbidity in newborns and often result in lifelong disabilities in survivors. Further elucidation of mechanisms that impact cerebral vascular damage may lead to therapies that will improve neurological outcome in neonates.